This study determined the impact of gender on substrate utilization during exercise at a self-selected pace. Healthy males (N = 17) and females (N = 17) performed a maximal exercise grade test and a 20-minute bout of treadmill walking at a preferred pace in order to determine fat and carbohydrate oxidation rates. Gas exchange measurements were performed throughout the tests and stoichiometric equations were used to calculate substrate oxidation rates. For each individual, a best-fit polynomial curve was constructed of fat oxidation rate versus exercise intensity (%VO2max) and used to obtain the following variables: (a) the maximal rate of fat oxidation measured over the entire range of exercise intensities; (b) the exercise intensity at which the maximal rate of fat oxidation was observed (Fatmax); and (c) Fatmax zone, a range of exercise intensities with fat oxidation rates equal to ±10% of Fatmax.

The maximal rate of fat oxidation was similar between men and women. However, the Fatmax was lower in men than in women. Similarly, the “low” and “high” borders of the Fatmax zone were lower in men than in women. During treadmill walking at a preferred pace, the carbohydrate oxidation rates were greater in men than in women, but there was no gender difference in the fat oxidation rates. The contribution of fat oxidation to total energy expenditure was greater in women than in men, despite no difference in the relative exercise intensity between them.

Implication. The contribution of fat oxidation to total energy expenditure is significantly greater in women than in men while performing at similar self-selected exercise intensities. Interestingly, both genders self-selected an exercise intensity that falls within the Fatmax zone.